identefying peak

[mmmd]

I am working on Sildenafil citrate (Viagra)
peaks are shown on 1.8 - 14.5 - 22 min
how would i recognise the peak of the substance
Mobile Acme:water 52:48
uv 280 nm Fr 1 C 40
peaks at 1.8 and 22 grows with concintartion
peak 14.5 is steady
please help

[tom jupille]

The usual procedure it to obtain a pure standard and run that.

It would be a good idea to run your detector at the absorbance maximum (291 nm) instead of 280 nm.

The peak at 1.8 minutes might be simply "t0 noise" (which can depend on the concentration of analyte). Try injecting a standard of something detectable but unretained (uracil is commonly used for this) to verify t0.

[Alexandre]

Try to reproduce the exact conditions from the literature – easiest way.

I guess the MS is not available.
Do a bit of literature research and try to find UV/VIS or FLD spectra.
If you have a scanning instrument then it is easy, if not, collect fraction and try to compare spectrum with the literature.

Remember how scientist in the past did investigation when there was no hi-tech.
Melting point, IR, cryo- and ebullioscopy are forgotten fiends…